The field of this invention relates to installation and assembly of large and heavy industrial machines, such as those installed at power utilities and manufacturing facilities.
In a preferred embodiment, the invention is a system for automatically predicting the proper adjustment height for support jacks underneath an industrial gas turbine to minimize distortion of the turbine due to gravity. Industrial gas turbines are large and heavy turbo machines that generate electrical power. These gas turbines typically weigh several tons. This enormous weight is sufficient to deform the gas turbine and cause misalignments of its components. For example, the deformation occurring during assembly of the gas turbine may cause the turbine's upper casing to not fit properly on the lower casing of the turbine. There is a need to provide supports for a gas turbine that compensate for deformation of the turbine due to gravity.
Gas turbines typically have modular casings for the compressor, combustor and turbine sections. Each casing module may have an upper and lower casing section that is assembled around the rotor components of the gas turbine. In a conventional assembly process, the lower half of the casings are installed on a concrete base or other platform. Jacks are positioned below the lower casing sections to support the gas turbine. The height of the jacks are adjustable to level the casing and correct for deformations in the casing. The jacks are necessary to compensate for the difference of flexural behavior when the top half casings are unbolted or absent compared for that with the upper half casings assembled. Such is the case when the rotor must be installed and aligned.
The amount of deformation in a gas turbine casing due to gravity may be on the order of millimeters or thousandths of an inch. This amount of deformation, especially in the lower casing of a gas turbine, is sufficient to cause difficulties in installing the rotor components into the casing and in aligning the upper casing onto the lower casing. In addition, once the gas turbine is assembled, its entire weight may cause further deformation of the top and lower sections of the casings. These further deformations may result in mis-aligned rotor components within the gas turbines, especially with respect to the clearance between the rotor blades and the blade shrouds formed by the casing sections. The rotor blades of the compressor and turbines rotate, and their tips travel in circular paths within the gas turbine. Certain stages have blade tips are closely surrounded by shrouds that surround the circular path of the blade tips.
If the casing shrouds are out-of-round due to deformation of the casing, then there will be shroud sections having too large of a gap from the tips of the blades. This gap in a compressor will allow compressed air to escape between the compressor stages. In the turbine, a gap may allow hot gases to escape from the turbine without acting on the turbine blades. The escaping air and gases resulting from the excessive gaps between the casing shroud and blade tips will degrade the efficiency of the gas turbines.
The gas turbine casing is supported by jacks underneath the casing. In addition, the height of each jack can been individually adjusted to level the casing and compensate for deformations in the casing due to gravity. Conventionally, the height adjustments of the jack have been done manually by technicians installing or reassembling the casing. The technicians use their experience and other empirical information to adjust the jacks properly under the gas turbine's lower casing. This manual procedure consists of (a) incrementally raising and lowering one or more jacks below the gas turbine, and (b) measuring distortion of the casing for the gas turbine, and repeating steps (a) and (b) until the measured casing distortion is reduced to acceptable levels.
As the rotor components and other sections of the gas turbine are installed in the lower casing, the jacks may be iteratively adjusted to correct for additional deformation and misalignments that occur in the casing and rotor components. Similarly, as the upper sections of the casing are aligned with the lower casing, the jacks may again be adjusted to align the lower casing with respect to the upper casing and allow the gas turbine assembly to be completed. The jack placements and height adjustments are done by technicians who use their levels, and other tools to determine whether the gas turbine casing or other components are out of alignment or deformed.
This conventional process is problematic. The manual jack placement and adjustment procedure is tedious, time-consuming and expensive. The procedure is prone to errors due to mis-measurement of casing distortions, misalignment of jacks underneath the gas turbine and incorrect height positioning of the jacks. Errors in positioning of jacks and setting their relative heights lead to deformations in the casing of a gas turbine which in turn results in poor efficiency. For example, it is estimated that an increase as little as 0.010 inch (0.025 cm) in the gap between a compressor/turbine blade and the casing shroud will result in a $50,000 per year in extra fuel costs for a single utility gas turbine at a typical power generation facility. This excessive fuel cost may be avoided by reducing the gap such that the clearance between a compressor/turbine blade tip and the casing shroud is within three-thousands inch (+/-0.003 in. and +/-0.0076 cm) of the intended clearance between shroud and blade.
There is a long-felt need for an improved technique for positioning jacks underneath a gas turbine casing and for adjusting the height of these jacks to minimize distortions in the casing due to gravity. Furthermore, there is a need for a method that automatically determines jack placement and jack height. There is also a desire for a jack adjustment method that will enable technicians during assembly or reassembly of a gas turbine to properly position jacks and adjust their height, without having to repeatedly measure casing deformation and readjust jack heights. Accordingly, there is a long-felt need for an automatic jack placement and jack height adjustment technique that is not prone to human errors, that does not require excessive amounts of time to arrange jacks and set their heights, and that minimizes casing distortions in gas turbines to improve the performance of the gas turbine.